feat: runtime provider hotswap (#82)

Add ability to replace a FeedSourceProvider at runtime and propagate
the new source to all active (and pending) user sessions, invalidating
their feed caches.

Co-authored-by: Ona <no-reply@ona.com>

packages/aelis-core/src/feed-engine.test.ts

@@ -180,6 +180,31 @@ describe("FeedEngine", () => {
 
 			expect(engine.refresh()).resolves.toBeDefined()
 		})
+
+		test("register invalidates feed cache", async () => {
+			const location = createLocationSource()
+			const engine = new FeedEngine().register(location)
+
+			await engine.refresh()
+			expect(engine.lastFeed()).not.toBeNull()
+
+			engine.register(createWeatherSource())
+
+			expect(engine.lastFeed()).toBeNull()
+		})
+
+		test("unregister invalidates feed cache", async () => {
+			const location = createLocationSource()
+			const weather = createWeatherSource()
+			const engine = new FeedEngine().register(location).register(weather)
+
+			await engine.refresh()
+			expect(engine.lastFeed()).not.toBeNull()
+
+			engine.unregister("weather")
+
+			expect(engine.lastFeed()).toBeNull()
+		})
 	})
 
 	describe("graph validation", () => {
@@ -934,4 +959,54 @@ describe("FeedEngine", () => {
 			engine.stop()
 		})
 	})
+
+	describe("invalidateCache", () => {
+		test("clears cached result", async () => {
+			const location = createLocationSource()
+			const engine = new FeedEngine().register(location)
+
+			await engine.refresh()
+			expect(engine.lastFeed()).not.toBeNull()
+
+			engine.invalidateCache()
+
+			expect(engine.lastFeed()).toBeNull()
+		})
+
+		test("is safe to call when no cache exists", () => {
+			const engine = new FeedEngine()
+
+			expect(() => engine.invalidateCache()).not.toThrow()
+			expect(engine.lastFeed()).toBeNull()
+		})
+	})
+
+	describe("isStarted", () => {
+		test("returns false before start", () => {
+			const engine = new FeedEngine()
+
+			expect(engine.isStarted()).toBe(false)
+		})
+
+		test("returns true after start", () => {
+			const location = createLocationSource()
+			const engine = new FeedEngine().register(location)
+
+			engine.start()
+
+			expect(engine.isStarted()).toBe(true)
+
+			engine.stop()
+		})
+
+		test("returns false after stop", () => {
+			const location = createLocationSource()
+			const engine = new FeedEngine().register(location)
+
+			engine.start()
+			engine.stop()
+
+			expect(engine.isStarted()).toBe(false)
+		})
+	})
 })

packages/aelis-core/src/feed-engine.ts

@@ -97,23 +97,33 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 	}
 
 	/**
-	 * Registers a FeedSource. Invalidates the cached graph.
+	 * Registers a FeedSource. Invalidates the cached graph and feed cache.
 	 */
 	register<TItem extends FeedItem>(source: FeedSource<TItem>): FeedEngine<TItems | TItem> {
 		this.sources.set(source.id, source)
 		this.graph = null
+		this.invalidateCache()
 		return this as FeedEngine<TItems | TItem>
 	}
 
 	/**
-	 * Unregisters a FeedSource by ID. Invalidates the cached graph.
+	 * Unregisters a FeedSource by ID. Invalidates the cached graph and feed cache.
 	 */
 	unregister(sourceId: string): this {
 		this.sources.delete(sourceId)
 		this.graph = null
+		this.invalidateCache()
 		return this
 	}
 
+	/**
+	 * Clears the cached feed result so the next access triggers a fresh refresh.
+	 */
+	invalidateCache(): void {
+		this.cachedResult = null
+		this.cachedAt = null
+	}
+
 	/**
 	 * Registers a post-processor. Processors run in registration order
 	 * after items are collected, on every update path.
@@ -249,6 +259,13 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 		this.cleanups = []
 	}
 
+	/**
+	 * Returns whether the engine is currently running reactive subscriptions.
+	 */
+	isStarted(): boolean {
+		return this.started
+	}
+
 	/**
 	 * Returns the current accumulated context.
 	 */